Lifetimes of elementary particles contain important information about the interactions that govern their decays. Theoretical models worthy of consideration must predict lifetimes, or ratios of lifetimes, accurately.
Decay time distributions are basically exponential but in neutral meson decays can be modified by both mixing and \(C\!P\)  violation. However, this is a crude way to learn about \(C\!P\)  violation.
One model, called the Heavy Quark Expansion, HQE, is used to determine \(|V_{cb}|\)  and \(|V_{ub}|\) . It can be tested by using its predictions for relative \(b\) -hadron lifetimes [1]}.
At lowest order the \(b\) -quark decay governs the lifetime, except for \(B_c\)  decays that are not covered here, but higher order corrections are important.
